1. Field of the Invention
The present invention relates to a compressed-air dental motor, consisting of a housing having a rotatably supported rotor arranged therein adapted to be set into rotation through compressed air introduced into the housing through the intermediary of a compressed-air inlet conduit; which includes a rotor shaft connectable with a tool, for instance a drill, wherein the compressed-air inlet conduit is associated with a valve arrangement located in the housing which is adapted to vary the compressed air infeed for each unit of time and which is controllable by means of a setting mechanism.
2. Discussion of the Prior Art
The compressed-air motor, for example, may in accordance with German laid-open patent application No. 19 41 159 be constructed as a turbine which has a rotor provided with blades; or pursuant to German published patent application No. 12 32 789 as a piston motor having a rotor provided with cylinders for pistons, for instance in the form of balls; or pursuant to German laid-open patent application No. 23 04 666 as a vane motor having a rotor which is provided with slits for receiving radially movable vanes.
In the compressed-air motor which has become known from German laid-open patent application No. 19 41 159, which is constructed as a turbine with a rotor equipped with blades wherein the compressed-air motor is only similar to the above-mentioned types. The setting mechanism consists of an electrical inductance coil located within the motor housing, in which there are induced voltage shocks through permanent magnets which are inserted in the rotor. At the loading of the work tool, the rotational speed of the rotor will reduce. This reduction in the rotational speed is transmitted through the inductance coil to a switch box arranged externally of the motor which includes an electrical control circuit, in the form of electrical amplitudes, and which emits an actuating amplitude, so as to be able to control in an electromagnetic manner the valve arrangement which is located within the compressed-air inlet conduit, also similarly arranged externally of the motor, for the purpose of varying the compressed air inlet to the motor for each unit of time. The arrangement, especially the switch box externally of the motor, demands special spatial requirements. Moreover, this known compressed air motor can only be employed in locations in which there is available an electrical connection.
In the compressed-air motor of the above-mentioned type which has become known through German published patent application No. 12 32 789, which is constructed as a piston motor with cylinders for pistons which, for example, are shaped as spheres, and, in a space-saving manner with the valve arrangement being located within the housing, the rated speed of the motor is presettable by varying the cross-section of the outlet aperture of the exhaust air, in effect, without necessity for an electrical connection. The exhaust air conduit includes a branch conduit which leads to a diaphragm chamber possessing a diaphragm which forms the adjusting arrangement, wherein the diaphragm exerts an effect on a slide valve which forms the valve arrangement. The adjusting arrangement which is constructed in this manner has the function thereof dependent upon the set cross-section of the exhaust air outlet aperture and, consequently serves only for the stabilizing of the rated speed of the motor. Particularly at a lower set rated speed, due to dependence upon the cross-section of the exhaust air outlet aperture it is not possible to obtain an increase in the torque at the loading of the work tool, since the therefore required additional compressed-air quantity to be introduced for each unit of time after passage through the displacement volume of the motor cannot pass as exhaust air through the mentioned cross-section of the exhaust air outlet aperture, thus possibly leading to the stalling of the motor. For the remainder, this known arrangement can only be employed with closed, or effectively, sealingly constructed types of air motors, but not with openly constructed compressed-air motors, such as are represented by vane motors, in which the rotor is set into rotation through "relaxing."
The vane motor which has become known through German laid-open patent application No. 23 04 666 does not at all include a valve arrangement which is controllable through a setting arrangement for varying the compressed air infeed for each unit of time, as a result of which this motor, which belongs to an entirely different class of construction, will stall upon the loading of the work tool.
The present invention thus proceeds as an improvement over the compressed-air motor which has become known from Germain laid-open patent application No. 12 32 789.